Question

1. explain watson and cricks double helix model of dna.

Explanation:

This model describes DNA as two complementary polynucleotide strands twisted into a right-handed double helix. The sugar-phosphate backbones run antiparallel (one 5'→3', the other 3'→5') on the outside. Nitrogenous bases pair internally: adenine (A) with thymine (T) via 2 hydrogen bonds, cytosine (C) with guanine (G) via 3 hydrogen bonds. The helix has a major and minor groove, and it is stabilized by base stacking and hydrogen bonding between complementary base pairs.

Answer:

Watson and Crick's double helix model of DNA is defined by the following key features:

1. Structure: A right-handed double helix composed of two polynucleotide strands.
2. Antiparallel Backbones: The sugar-phosphate backbones of the two strands run in opposite directions (one strand is oriented 5' to 3', the other 3' to 5') and form the outer framework of the helix.
3. Complementary Base Pairing: Nitrogenous bases are located inside the helix, with specific pairing: adenine (A) exclusively bonds to thymine (T) via 2 hydrogen bonds, and cytosine (C) exclusively bonds to guanine (G) via 3 hydrogen bonds.
4. Grooves: The helix has a wider major groove and a narrower minor groove, which are important for protein-DNA interactions.
5. Stability: The structure is stabilized by hydrogen bonding between complementary base pairs and hydrophobic base stacking interactions along the axis of the helix.